FIG. 1 is a schematic view showing a non-closed type forced cooling frequency converter in the prior art. As shown in FIG. 1, the conventional frequency converter of motor blows the cooling air to a heat sink 202 using a fan 201, and it also blows the cooling air to each elements in the circuit board simultaneously, resulting in the impurities in the air blown into the circuit board and contaminating internal devices, pins and pads, so that each elements in the circuit board has a potential risk to be short-circuit or damaged. Meanwhile, the safety distance between respective elements in the circuit board depends on the contamination degree that the circuit board might suffer, i.e., the more contamination, the greater safety distance is required, which adversely affect the size reduction of the frequency converter.
FIG. 2 is a schematic view showing a frequency converter in which main heat-generating element and a part of secondary heat-generating elements are forced cooled while the other secondary heat-generating elements are natural cooled. As shown in FIG. 2, the conventional frequency converter of motor usually employs a combination cooling method of the fan forced cooling and the natural cooling through heat-dissipating holes, i.e. the power element such as the Insulating Gate Bipolar Transistor (IGBT) is forced cooled by the heat sink 202 and the fan 201, while the secondary heat-generating elements are natural cooled or a small amount of wind is blown to capacitors 111 and coils etc. Thus, poor heat dissipation for elements may reduce lifetime of the elements, thereby resulting in reduction of the lifetime of the whole frequency converter of motor.
In the frequency converter of the prior art, there is no effective thermal insulation measures to be taken between main heat-generating element and other elements on the circuit board, as well as between the heat sink and the circuit board, and the heat conduction of the main heat-generating element and the heat sink may still make other elements on the circuit board to operate under high temperature.
In addition, aligning connection is performed between IGBT and the heat sink and between IGBT and the circuit board, which is generally achieved via aligning holes on the circuit board, the heat sink and IGBT. However, in the assembly process, IGBT is usually adhered to the backboard of the heat sink by heat conductive silica gel, and then pressed on the circuit board. However adhering IGBT on the heat sink may cause position deflection and rotation, thereby influencing the alignment between IGBT, the heat sink and the circuit board.
Therefore, it is necessary that each heat-generating elements of the frequency converter of motor is effectively heat-dissipated, and the heat-generating elements are heat insulated with other elements on the circuit board, so as to improve operation quality and lifetime of the product. Also, the problem of aligning positioning between IGBT and the heat sink and the circuit board need be solved.